A pillow is a soft cushion you rest your head on while sleeping or relaxing. Most pillows are fabric bags filled with feathers, foam, or synthetic material that compress under the weight of your head, making sleep more comfortable. Without a pillow, your neck might bend at an awkward angle on a flat mattress, which would hurt after a while.

People have used pillows for thousands of years, though ancient pillows weren't always soft. In ancient Egypt, wealthy people used carved stone headrests, while the Chinese sometimes used hard wooden pillows. The soft, comfortable pillows we know today became common in Europe during the Middle Ages.

The word can also describe anything that cushions or softens impact. In a pillow fight, people playfully whack each other with pillows. Engineers talk about an air pillow when they mean a cushion of air that protects something. If you pillow your head on your arms at your desk, you're using your arms as a makeshift pillow during a quick rest.